1. Field of the Invention
This invention relates to the removal of color from organic waste liquor, and in particular is concerned with color removal from thermally conditioned sludge liquors.
2. Information Disclosure Statement
The liquor obtained in the dewatering of thermally conditioned organic sludge, especially sewage sludge, is generally a small volume stream of concentrated, highly colored material. The liquor to be treated is obtained by wet air oxidation of organic sludges by methods known in the art; cf. U.S. Pat. Nos. 3,272,739, 3,272,740 and 3,359,200. These liquors are generally treated by recycling them to the treatment plant influent for dilution with raw wastewater and subsequent biological or biophysical treatment within the system. The concentrated nature of these thermally conditioned liquors can put additional loading on the plant, in the form of organic components and color materials which require removal from the wastewater. Treatment plants often are required to meet specific discharge requirements with respect to effluent color, BOD.sub.5, suspended solids, etc. If these limits are exceeded, stiff penalties are enforced.
Various treatment methods have been disclosed which remove the organic and/or color content of thermally conditioned sludge liquors. In U.S Pat. No. 3,874,168 Erickson et al. disclose a separate highly loaded biological treatment process to treat thermally conditioned sludge liquors. This process requires much additional hardware for operation.
U.S. Pat. No. 4,626,354 by Hoffman et al. discloses biophysical anaerobic treatment of thermally conditioned sludge liquor using a powdered adsorbent, such as activated carbon, within the anaerobic digester system. Once subjected to anaerobic digestion, the treated liquor is more amenable to color removal by adsorption with fresh powdered adsorbent. Again, a separate system is dedicated to treatment of thermally conditioned sludge liquors.
Applicant has discovered a simple treatment process which effectively removes a substantial portion of the color and organic constituents present in thermally conditioned sludge liquors with a minimum or additional equipment.